The present disclosure relates to processes for preparing rubber compositions and articles made therefrom.
The use of silica/silane-filler systems to reduce the rolling resistance and improve the wet traction of passenger car tires is well known in the art. A reduction of rolling resistance, and therefore less fuel consumption, while improving handling, wear and wet and dry traction, continues to be the subject of much technical investigation and development.
Polysulfurized alkoxysilanes, such as bis(triethoxysilylpropyl)tetrasulfite (TESPT) and blocked mercapto-functional silanes such as 3-octanoylthio-1-propyltriethoxysilane are currently the most effective, and therefore the most widely used, coupling agents in rubber compositions intended for tires, especially those compositions containing styrene-butadiene rubber or butadiene rubber. The processing of polysulfurized alkoxysilanes tends to be poor, as reflected by scorch, due to the high reactivity of the polysulfide functional group and its ability to donate sulfur, a curative, during mixing. Rubber formulations containing silica and polysulfurized alkoxysilanes require multiple non-productive mixing cycles at low temperatures and may still partially cure during these mixing operations generating waste, both of which drawbacks can add significantly to production costs.
Although blocked mercapto-functional silanes eliminate many of the problems associated with processing silica-reinforced tires, these compounds often fail to achieve the levels of reinforcing efficiency and abrasion resistance desired by the tire industry due, it is thought, to the silane only partially reacting with the filler surface. Consequently, the silane is only partially effective at dispersing the filler, e.g. silica, into the rubber matrix, especially early in the non-productive mixing step. The blocking group may also be only partially removed during the productive mixing step. Both good filler dispersion and good filler coupling to the rubber are required to achieve satisfactory end-use properties.
A process for preparing a rubber composition that uses thiocarboxyl-functional silane coupling and/or dispersion agent in rubber applications while still exhibiting the properties of low scorch and improved filler dispersion and coupling of the filler to the rubber matrix would therefore be highly desirable.